Question: You have found the following ages (in years) of 4 tigers. The tigers are randomly selected from the 40 tigers at your local zoo: $ 15,\enspace 18,\enspace 3,\enspace 18$ Based on your sample, what is the average age of the tigers? What is the variance? You may round your answers to the nearest tenth.
Because we only have data for a small sample of the 40 tigers, we are only able to estimate the population mean and variance by finding the sample mean $({\overline{x}})$ and sample variance $({s^2})$ To find the sample mean , add up the values of all $4$ samples and divide by $4$ $ {\overline{x}} = \dfrac{\sum\limits_{i=1}^{{n}} x_i}{{n}} = \dfrac{\sum\limits_{i=1}^{{4}} x_i}{{4$ To compensate for this underestimation, rather than simply averaging the squared deviations from the mean , we total them and divide by $n - 1$ $ {s^2} = \dfrac{\sum\limits_{i=1}^{{n}} (x_i - {\overline{x}})^2}{{n - 1}} $ $ {s^2} = \dfrac{{2.25} + {20.25} + {110.25} + {20.25}} {{4 - 1}} $ $ {s^2} = \dfrac{{153}}{{3}} = {51\text{ years}^2} $ We can estimate that the average tiger at the zoo is 13.5 years old. There is a variance of 51 years $^2$.